Amplifier for pulses



June 4, 1946. .T T EATQN ET AL Z@ AMPLIFIER FOR PULSES l I Filed Sept. l1, 1942 PULS'S or w. i

/10 v j y/A11 /lf2 3 PULSE Ala/sf.' ou'fpuw HMB ib- PULSE OUTPUT 6 y n l R www WHY #EPE/WE1? Patented June .4, i946 n. al. R FOB PULSES Thomas T. Eaton, Haddon Heights, and David G. C. Luck, Merchantville, N. I.. assignors to Radio Corporation of America, a corporation of Delaapplication september 11, i942, serial Ne. 457,968

' (ci. ris-44) d Cla. i

Uur invention relates to noise reducing circuits for non-sinusoidal electric waves and particularly to an amplifier or noise reducing circuit for the amplification or transfer of periodically recurring electrical. pulses. Y

An object of the invention is to provide an improved method of and means for improving the signal-to-noise ratio of a non-sinusoidal signal.

A further object of the invention is to provide an Hence, if an amplifier or other signal transferring circuit is designed to have a comparatively high gain for these frequency components and a comparatively low gain for undesired signals coni-` prising other frequency components, it is evident -th'at the amplifier will pass the desired pulses or -the plate circuit of an amplifier tube so that the plate circuit impedance depends upon the input impedance of the delay circuit. It is a. well known characteristic of such a line that it will have maximum input impedance at a certain funda'- mental frequency and at the harmonic frequencies and have a comparatively low input impedance at other frequencies. Since the amplifier gain is equal to the Imutual conductance of the tube times the plate circuit impedance it follows that our improved amplifier may be designed to pass the frequency components of a pulse or the like and reject noise or other interfering signals.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which.

Fig. 1 is a block diagram of a pulse receiver which includes an amplifier designed in accordance with the invention, Fig. 2 is a circuit dia gram of an ampliiier embodying the invention, Figs. 3 and 4 are graphs that are referred to in explaining` the invention, and Figs. 5 and 6 are diagrams of other embodiments of the invention.

' shown'at 25. l

2 reducing amplier i2 designed in accordance with the invention. and a video frequency amplifier i3.

Fig. 2 shows one embodiment of the noise reducing amplifier I2. It comprises an amplifier tube I6 which may be of the pentode type having a cathode i6, a control grid ii,`a screen grid i8, a suppressor grid i9 and an anode 2i. The input circuit of the tube ii includes'a grid capacitor 22, a grid leak resistor 23 and a bypassed cathode biasing resistor 2d. Apositive v:i1-C. voltage is applied to the screen grid i9 through the usual filter comprising a resistor 26 and a filter capacitor 27. The plate circuit of tube it includes a plate resistor 28 or other impedance unit through which operating voltage is applied to the anode 2|. A bypass or filter capacitor is -An open-ended delay circuit 29 has its input end connected across the plate resistor 28. In this specific example circuit 29 is in the form of a low-pass filter having series inductance coils 3| and shunt capacitors 32. The other end of lfilter 29 will reiiect signal components since it is not terminated for non-reflection. Also, the reected components will again be reflectedA at the input end of iilte'r 29 because the resistance lof In. the several gures like parts are indicated by 'radio pulse receiver I0, a detector ii, a noise resistor 28 is made large compared with the surge impedance of the filter. For example, the' surge impedance of -iilter 29 may be 1000 ohms and the resistance of resistor 28 maybe 20,000 ohms. As a result, the impedance looking into lter 29 from tube I4 varies .with frequency as shown in Fig. 4. It is evident that the amplifier voutput taken off the plate resistor will be small except at a particular frequency and its harmonics.

As previously stated, periodically recurring non-sinusoidal waves, such as the pulses shown in Fig. 3, consist of fundamental and harmonic frequency components. 1t` is evident that the plate circuit of the amplifier tube It may be defrequencies of any particular non-sinusoidal wave that it is desired to amplify. The .impedance peaks will occur at such frequencies if thedelay If the pulse repetition rate is low enough to require the use of a long delay line or circuit: the

delay line attenuation may be great enough to make desirable the use of a two-way repeater 36 'pas shown.' in Fig. 5. The repeater 3l is of well known design and in the specific example illustrated is located in the middle of the delay circuit 29. By using the repeater 3i the impedance Fig. 6, for example, the vacuum tube il may bev replaced by a high impedance resistor 35. Also, the delay circuit 29 may be coupled through a transformer l1 to the signal `trani'derring circuit which includes resistor I5. The delay circuit may, of course,be a lineV having distributed capacity and inductance.

We claim` as our invention:

1. In apparatus for transferring a non-sinusoidal periodic signal, a signal transferring circuit comprising a vacuum tube having an anode circuit, and an open-ended delay circuit having input terminals connected to said anode circuit, the impedance of said anode circuit looking into it from said input terminals being comparatively high and the surge impedance of said delay circuit looking into it from said input terminals being comparatively low, said delay circuit providing the proper-.amount of delay for the fundamental and harmonic frequency components of said signal to make the impedance of said anode 30 circuit at said input terminals the maximum at said frequencies, and means for taking signal od said input terminals.

2. An amplifier for amplifying periodically re- .4 amplifier comprising an amplifier tube having an anode circuit, an anode impedance element y cuz-ring waves of non-sinusoidal wave form, said 35 in said circuit and a delay circuit which has one .end thereof connected across said anode imped-` ance element and which has the other end open to cause reiiections, the impedance of said de impedance element being several times theasge impedance of said delay circuit whereby the is reection at both ends of said delay circuit.A

3. In a circuit for transfen'ing a non-sinusoidal periodic signal having fundamental and harmonic frequency components, a vacuum tube having an output circuit, and a delay circuit having one end connected to said output circuit, said delay circuit being reiiecting at both ends and having a delay characteristic suchjthat the said frequency components appearing at said one end of the delay circuit both before and'after reiiectionv are in phase whereby the impedance of said anode circuit is the maximum at said frequencies.

4. An ampliiier for amplifying periodically recurring waves of non-sinusoidal wave form, said amplifier comprising an amplifier tube having an anode circuit, an anode impedance element in said circuit and a delay circuit which has one end thereof connected across saidvanode impedance element and which has the other end open to cause reflections, the impedance of said element being several times the surge impedance of said delay circuit, and at least one two-way repeater connected in said delay circuit at some point intermediate its ends.

'moms T. EATON. navm G. c. Loon 

